Electrical resistor



Aug. 29, 1933. H. L. BRADLEY ELECTRICAL RESISTOR Filed June 24. 1929 2Sheets-Sheet 1 1933. H. L. BRADLEY 1,924,105

ELECTRICAL RESISTOR Filed June 24. 1929 2 Sheets-Sheet 2 I v M/deesfw IL5; 14 J% /7 /Z. 5/7177; i dmm Patented Aug. 29, 1933 UNITED STATESPATENT OFFICE ELECTRICAL RESISTOR consin Application June 24, 1929.Serial No. 373,399

11 Claims. (01. 201-50) This invention relates to certain new and usefulimprovements in variable resistors and refers more particularly tovoltage dividers or potentiometers. As is well known in the art,potentiometers consist of a pair of resistor units, the

resistance of which is simultaneously and inversely varied and in thepresent invention the resistor units are composed of quantities of com-'pressible powdered material having the desired conductivecharacteristics as in a co-pending application Serial No. 321,336 filed,November 23, 1928.

It is an object of this invention to provide a potentiometer ofsimplified and compact design to be particularly adaptable for use inradio receivers.

Another object of this invention resides in the provision of an improvedpotentiometer in which the resistor units are arranged on a common1ongitudinal axis and have a common means for varying their resistance.

Another object of this invention resides in the provision of apotentiometer having a pair of resistor units mounted on a commonlongitudiapplying member which simultaneously regulates the pressure onboth units.

A further object of this invention resides in the provision of animproved potentiometer having a shaft extending through both resistorunits for actuating a common pressure member and which likewise providesmeans for securing the elements assembled.

And a still further object of this invention resides in the provision ofa potentiometer having a casing with a plunger disposed transversely andmedially thereof to divide the same into separated compartments whichare filled with powdered resistance material whereby movement of theplunger increases the pressure on the resistance material at one sidethereof and decreases the pressure on the material at the other sideand. vice versa.

With the above and other objects in view which will appear as thedescription proceeds, my

invention resides in the novel construction, combination and arrangementof parts substantially as hereinafter described and more particularlydefined by the appended claims, it being understood that such changes inthe precise embodiment of the hereindisclosed invention may be made ascome within the scope of the claims.

In the accompanying drawings, I have illustrated two complete examplesof the physical embodiment of my invention constructed accordnal axisand separated by a movable pressure' ing to the best mode I have so fardevised for the practical application of the principles thereof, and inwhich:

Figure 1 is a transverse, sectional view taken through a potentiometerembodying my invention with parts in elevation;

Figure 2 is a cross sectional view taken thrgaugh Figure l on the planeof the line 22, an

Figure 3 is a fragmentary, sectional view taken through Figure 2 on theplane of the line 3-3.

Figure 4 is a view similar to Figure 1 illustrating a slightly modifiedform of my invention;

Figure 5 is a viewpartly in section and partly in elevation, takenthrough Figure 4 on the 7 plane of the line 5-5, and

Figure 6 is a fragmentary detail view taken through Figure 5 on theplane of the line 6-6.

Referring now more particularly to the accompanying drawings, in whichlike numerals designate like parts throughout the several views, nu-

..,merals 5 and 6, respectively, designate an upper The shaft 10 has anenlarged exteriorly s5 threaded portion 11 formed thereon, which issubstantially equi-distant from the ends of the sections 5 and 6, anddisposed between the ends of central projections or bosses 12 and 13carried by the casing sections 5 and 6, respectively, and through whichthe shaft projects. The lowermost end of the shaft is reduced at a pointin line with the bottom of a counter-bore 14 formed in the outer end ofthe section 6 to receive a washer 15 which is secured thereon byriveting or the like to maintain the shaft freely rotatable butnon-longitudinally movably assembled with the section 6.

The bottom of the cup-shaped section 6 is substantially covered by ametal washer or apertured plate 16 which is secured in position byrivets 17, one of which also passes through one end of a terminal lug 18to electrically connect the same with the plate. A recess 19 formed inthe outer bottom of the section receives the terminal lug 18 and thusprevents turning thereof about its attaching rivet 17.

The terminal 18 forms one of the end terminals of the potentiometer andthrough the plate 16 is electrically connected with the one of the renosistor units which consists of a quantity of powdered resistancematerial substantially filling the section 6. The other resistor unit 21is likewise formed of powdered resistance material and is disposed inthe upper section 5 being electrically connected with the other endterminal 22 in a similar manner through a plate 23 likewise secured inthe bottom of the section 5, as clearly ilustrated in Figure l. Theterminal 22 like the terminal 18 is prevented from turning about itspoint of securement by being disposed within a recess 24 formed in theupper outer face of the section 5.

;The units 20 and 21 are separated by a plunger 25 threaded on theportion 11 of the shaft and comprising a metal disc 26 on each side ofwhich a washer or disc 27 of larger diameter and formed of felt or othersimilar material, is disposed. Metallic discs 28 tied together by rivets29 or the like maintain the felt washers assembled with the disc 26. Asthe diameter of the felt washers is sufliciently large to have a snugengagement with the walls of the casing sections it will be seen that asthe shaft 10 is rotated by means of a knob or the like 30 fixed to itsouter end, the frictional engagement of the felt discs with the casingwalls holds the plunger against rotation to effect longitudinal movementthereof, which simultaneously and inversely varies the pressure on theresistor units 20 and 21 and thus increases or decreases theirresistance.

The aperture 8 in the casing section 5 through which the upper end ofthe shaft 10 extends is larger than the opening 9 in the section 6 andhas its inner end provided with a hexagonally shaped counter-bore 31 andwith a second comparatively shallow counter-bore 32. A metal sleeve orbushing 33 having a hexagonal head or flange and whose aperture is suchas to snugly receive the shaft 10 extends through the aperture 8 and hasits head or flange disposed in the hexagonal counter-bore 31 to preventturning of the bushing.

The enlarged apertured end of a terminal lug 34 through which thebushing 33 extends is also received in the counter-bore 31, beingimpinged between the bottom of the counter-bore and the 'head of thebushing. The other end of the terminal 34 extends through an opening 35in communication with the counter-bore 31, and is confined in a recess36 with its end projecting beyond the periphery of the casing to providethe neutral or central terminal of the potentiometer, which ,iselectrically connected with the plunger 25, through the bushing 33 andthe shaft 10 and thus with the adjacent faces of the resistor units.

The bushing 33 and consequently the terminal lug 34 are maintained inposition by a second bushing 37 formed of insulating material andconstituting the projection 12 which engages the upper end of thethreaded portion 11. The upper end of the bushing 37 has a steppedflange 38, the outermost portion of which is received in the shallowcounter-bore 32 confining the hexagonal head of the bushing 33 in itshexagonal counter-bore. Displacement of the bushing 37 is prevented bythe washer 23 whose inner periphery engages the smaller stepped portionof the flange 38 and thus extends over the outer larger portion. In thismanner the attachment of the plate or washer 23 in the bottom of thecasing section 6 secures the bushings 33 and 37 and the terminal lug 34against displacement.

In assembling the potentiometer the lower half of the casing or section6 in which the shaft 10 has been secured, is filled with the desiredquantity of powdered resistance material and the plunger 25 is thenthreaded on the shaft which closes the section open end and permits thesame to be turned to insert the shaft through the casing section 5 whichhas also been filled with the proper amount of powdered material. Afterthe sections are engaged with each other a split ring 39 is secured inan annular recess 40 formed in the shaft at a point adjacent the end ofthe bushing 33 which thus holds the sections against separation.

The projected end of the bushing 33 is preferably threaded to receive aclamp nut 41 by which the device may be clamped to any suitable panelsupport in the conventional manner.

In use, the felt washers 27 of the plunger never pass the line of jointbetween the casing sections 5 and 6 thereby preventing the possible lossof powdered material between the casing sections without necessitatingthe provision of means for providing a tight joint therebetween.

In the structure described, it is possible that an extreme degree ofcompression will cause a resistor element to retain its compressed stateand create a space between it and the plunger when the plunger is movedin the opposite direction. This is objectionable as it would interruptthe circuit, and therefore, the modification depicted in Figures 4, 5and 6, is so designed that an electrical connection is always maintainedbetween the outer terminals and the central or neutral terminal.

In this form of the invention, the construction and assembly of theseveral elements is materially simplified. The spindle 10 which isrotatably but non-longitudinally movably assembled with the casingsection 6 is journaled in a bushing 42 mounted in the aperture 9 withits lower flange 43 positioned in the counterbore 14. The upper end ofthe bushing is extended through an apertured flange 44 which ispreferably of hexagonal shape and recessed in the bottom of the casing,to be swedged over, as at 45, to secure the bushing and the flange inposition.

A ring 46 is secured in an annular groove 4'1 formed in the bottom ofthe casing adjacent its outer periphery, by rivets 43 or the like, oneof which passes through the terminal 18 so that the resistor unit orelement 20 electrically connects the annular ring 46, and the hexagonalflange 44.

The aperture 8 in the casing section 5, through which the upper end ofthe spindle 10 extends, mounts a bushing 49, on the lower end of which ahexagonal flange 50 is formed to be received in a similarly formedrecess in the bottom of the casing, a swedged over portion 51maintaining the bushing 49 assembled with the casing section 5. Thebushing 49 takes the place of bushng 33 of that form of my inventionillustrated in Figures 1 to 3, and likewise has its outer end threadedto receive the nut 41 by which the device is clamped to a suitable panelor the like. The casing section 5, like the section 6, also has a ring46 secured in a groove 47 with the terminal 22 electrically connectedtherewith through one of its securing rivets 48.

The construction of the plunger 25 is also simplified and consists of adisc or plate 52 having a central hub 53 pressed therefrom which ispassed through an aperture in a second disc 54 and is riveted over itsouter face to maintain the axial shaft extending through the casingsections discs against separation, a felt washer 55 being impingedbetween the two discs. The neutral terminal 34 which is electricallyconnectedwith the shaft or spindle 10 and thus with the hexagonalflanges 44 and '50, has its;

innerapertured end 56 impinged between the flange 43 of the bushing 42and the bottom of the counterbore14, see Figure 6.

Thus-it -wi1l-be seen that as the circuit from the neutral terminal toeither of the outer terminals is completed by the resistorv elementsbridging the space between the rings 46 and the flanges 44 and 50, thecircuit remains unbroken at all times.

From the foregoing description, taken in connection with theaccompanying drawings, it will be readily apparent to those skilledin'the art to which an invention of the character described appertains,that I provide an improved potentiometer which isextremely compact andin which strainis never placed on the'panel, nor is there ever atendency to spread the two casing sections, as all strains are absorbedby the shaft. For instance, in Figure 1, the parts are illustrated inthe positions at which the upper resistance unit 21 is under maximumcompression between the end wall of the casing section 5 and the plungerand as the plunger is threaded on the shaft and the shaft is retainedagainst longitudinal movement with respect to the section, through thesplit ring 39 and the bushing 33, all strains are retained within theconfines of the upper casing and in no way impart any stress to thelower casing.

Furthermore, it will be obvious that the adjustment of the resistancevalues of its units may be readily and quickly accomplished withoutlongitudinal movement of the adjusting screw.

What I claim as my invention is:

1. In a potentiometer of the character described, a casing comprisingaxially aligned sections, a compressible resistor element in eachsection, a pressure member separating the resistor elements, a memberextending through both sections to secure the same against separation,and means whereby said second member serves to actuate the pressuremember to simultaneously and inversely vary the resistance of theresistor elements. V

2. In a potentiometer of the character described, a casing comprisingaxially aligned sections, a compressible resistor element in eachsection, a pressure member operable to simultaneously and inversely varythe resistance of the resistor elements, and a single means foractuating the pressure member and securing the casing sections together.

3. In a potentiometer of the character described, a casing comprisingaxially aligned sections, a compressible resistor element disposedwithin each section, a pressure member operable to compress eitherresistor element between it and its respective casing section end wall,a member axially aligned with the resistor elements and the casingsections for actuating thepressure member, and means whereby the strainsincidental to the compression of either resistor element are carried bythe actuating member.

4. In a potentiometer of the character described, a casing comprisingaxially aligned sections, a compressible resistor element disposedwithin each section, a pressure member operable to compress eitherresistor element between it and its respective casing section end wall,an

and threaded in the pressure member whereby rotation of the shaftactuates the pressure member. andmeans connecting the shaft with eachcasing section wherebythe strains incidental to the compression of eachresistor element are carried by the shaft and the respective sectionwithout imparting stress to the other section.

5. An-electrical resistance device comprising, an adjusting element, amovable member mounted on the medial portion of the adjusting element,means for moving saidmember axially with respect to the adjustingelement upon rotation of the adjusting element, compressible resistorelements on opposite sides of said "movable member, and abutments on.the end portions of the adjusting elements outwardly of the resistorelements, and between which and said movable member the resistorelements are compressible upon movement of the movable member,

6. An electrical resistance device comprising, compressible resistorelements, an adjusting element extending axially through the resistanceelements, and provided with a screw thread, a movable member mounted onsaid screw thread and separating the resistance elements, abutmentsconnected with the end portions of the adjusting element and engagedwith the resistance elements whereby each element is confined betweenone abutment and said movable member, rotation of the adjusting elementin one direction moving said movable member toward one abutment tocompress one resistance element and relieve the pressure of the otherand vice versa.

7. An electrical resistance device comprising compressible resistanceelements, an adjusting element extending through said resistanceelements, a movable member mounted on the medial portion of saidadjusting element and separating the resistance elements from eachother, means whereby rotation of the adjusting element imparts movementto said member axially with respect to the adjusting element, casingsections enclosing the resistance elements, and means for holding thecasing sections against axial movement with respect to the adjustingelement whereby movement of said movable memberupon rotation of theadjusting element-in one direction compresses one of the resistanceelements between it and one casing section and movement of said memberin the other directionupon opposite rotation of the adjusting element--compresses the other resistance element between it and the other casingsection.

8. An electrical resistance device comprising, a pair of compressibleresistor elements having a common axis, a pressure member between theresistor elements and engaged with their adjacent faces, fixed wallsbetween which and the pressure member the resistor elements arecompressible, an adjusting shaft extending through the resistor elementsand the pressure member, and having a threaded connection with thepressure member, and supporting means for the shaft fixed with respectto said fixed walls and with which the shaft has a freely rotatable butnon-longitudinally movable connection whereby rotation of the shaftmoves the pressure member toward one fixed wall or the other.

9. An electrical resistance device comprising, a pair of compressibleresistor elements having a common axis, a pressure member between theresistor elements and engaged with their adjacent faces, fixed wallsbetween which and the pressure member the resistor elements arecompressible, an adjusting shaft extending through one resistor unit andhaving a threaded connection with the pressure member, and supportingmeans for the shaft fixed with respect to said fixed walls and withwhich the shaft has a freely rotatable but non-longitudinally movableconnection, whereby rotation of the shaft moves the pressure membertoward one fixed wall or the other.

10. An electrical resistance device comprising, a pair of axiallyaligned compressible resistor elements, a pressure member between theresistor elements and engaged with the adjacent faces thereof, anadjusting member co-axial with the common axis of the resistor elementsand having a threaded connection with the pressure member, an enclosingcasing having spaced walls substantially parallel with each other andthe pressure member and engaging the resistor elements to cooperate withthe pressure member to compress the resistor element, and means freelyrotatably,

but non-longitudinally movablyconnecting the adjusting member with thecasing spaced walls, whereby the pressure membermay be readily adjustedby rotation of the adjusting member to vary the degree of compression ofthe resistor elements.

11. An electrical resistance device comprising, a pair of compressibleaxially aligned resistor elements, a pressure member between theresistor elements and engaged with their adjacent faces, fixed wallsengaging the opposite faces of the resistor elements and between whichand the pressure member the resistor elements are compressible, anadjusting shaft in substantially axial alignment with the common axis ofthe resistor elements and connected with the pressure member so thatmovement of the adjusting shaft in one direction or the other moves thepressure member toward one fixed wall or the other, a support for theadjusting shaft fixed with respect to the fixed walls, and means formoving the adjusting shaft.

HARRY L. BRADLEY.

